• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 63 subscribers
  • Views 1113 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS2379 Adapter input priority circuit

Ed Walker
Prodigy 5 points
Other Parts Discussed in Thread: TPS2379, TPS2378

I am using TPS2379 in a 50W PoE system.
I have a 48V adapter input per OPTION 1 in slva306a, before the TPS2379.
     
Also using the CDB function of TPS2379.

I want to add adapter priority like the TPS2378 has.
However TPS2378 has APD function on the same pin as TPS2379 CDB pin.

Is there a way to implement adapter priority with OPTION 1 oring on the TPS2379?

  • 0
    TI__Mastermind 41790 points
    Hi Ed,

    For option 1, VAdatper>VPoE will work for adapter priority. Otherwise, the only solution would be to have a pass FET and logic circuit that removes PoE when an adapter is present.

    Regards,
    Darwin
  • 0 in reply to Darwin Fernandez
    Prodigy 5 points
    Thank you Darwin, do we have that pass fet and logic circuit that can be used in this case?
  • 0 in reply to Ed Walker
    TI__Mastermind 41790 points
    Hi Ed,

    After going through this exercise, I found a logic circuit solution would be possible if there was a biasing voltage present in the system. I doubt this the case in customer's design as the system voltage will have to come from either PoE or adapter.

    So, instead, I believe the more practical solution would be to implement option 2 oring and pull DEN down similar to Figure 10 in the SLVA306A app note. Luckily since the adapter is on the primary side, you wouldn't need to use an opto.
  • 0 in reply to Darwin Fernandez
    Expert 1430 points

    Hi Darwin,

       

    We do not have a biasing voltage.  System voltage will come from PoE or adapter.

     

    We need the higher current capabilities of TPS2379 - but it does not have the DEN pin.

     

    A work-around would be to wire in 48VDC into the PoE RJ-45.  This works for our V60 PoE+ design, but for our other project we want up to 50W.  Would this still work?

    Thanks for your help.

  • 0 in reply to TIguru
    TI__Mastermind 41790 points
    Hi TIguru,

    TPS2379 does have a DEN pin as shown in its datasheet. Figure 10 of SLVA306 is still a viable solution. And you wouldn't need an opto. Just a FET and resistor divider.

    Regards,
    Darwin